Electromechanical spatial light modulators with a variety of designs have been used in applications such as display, optical processing, printing, optical data storage and spectroscopy. These modulators produce spatial variations in the phase and/or amplitude of an incident beam of light using arrays of individually addressable devices.
Spatial phase modulation of an incident beam can be accomplished by arrays of individually addressable deformable mirrors. Such devices can be from a deformable reflective membrane suspended over a grid of supports, as described in U.S. Pat. No. 4,441,791, issued Apr. 10, 1984 to Hornbeck, entitled "Deformable Mirror Light Modulator." However, because of the membrane and support structure, these particular deformable mirrors are very inefficient. More efficient deformable mirror designs are disclosed in U.S Pat. No. 5,170,283, issued Dec. 8, 1992 to O'Brien et al., entitled "Silicon Spatial Light Modulator," and in U.S. Pat. No. 5,844,711, issued Dec. 1, 1998 to Long, Jr., entitled "Tunable Spatial Light Modulator."
Another class of electromechanical spatial light modulators has devices with a periodic sequence of reflective elements that form electromechanical phase gratings. In such devices, the incident light beam is selectively reflected or diffracted into a number of discrete orders. Depending on the application, one or more of these diffracted orders may be collected and used by the optical system. For many applications, electromechanical phase gratings are preferable to deformable mirrors. Electromechanical phase gratings can be formed in metallized elastomer gels; sec U.S. Pat. No. 4,626,920, issued Dec. 2, 1986 to Glenn, entitled "Solid State Light Modulator Structure," and U.S. Pat. No. 4,857,978, issued Aug. 15, 1989 to Goldburt et al., entitled "Solid State Light Modulator Incorporating Metallized Gel and Method of Metallization." The electrodes below the elastomer are patterned so that the application of a voltage deforms the elastomer producing a nearly sinusoidal phase grating. These types of devices have been successfully used in color projection displays; see "Metallized viscoelastic control layers for light-valve projection displays," Displays 16, 1995, pages 13-20, and "Full-colour diffraction-based optical system for light-valve projection displays," Displays 16, 1995, pages 27-34.
An electromechanical phase grating with a much faster response time can be made of suspended micromechanical ribbon elements, as described in U.S. Pat. No. 5,311,360, issued May 10, 1994, to Bloom et al., entitled "Method and Apparatus for Modulating a Light Beam." This device, also known as a grating light valve (GLV), can be fabricated with CMOS-like processes on silicon. Improvements in the device were later described by Bloom et al. that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbons and the substrate, and 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast. See U.S. Pat. No. 5,459,610, issued Oct. 17, 1995 to Bloom et al., entitled "Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate." Bloom et al. also presented a method for fabricating the device; see U.S. Pat. No. 5,677,783, issued Oct. 14, 1997, entitled "Method of Making a Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate." Additional improvements in the design and fabrication of the GLV were described in U.S. Pat. No. 5,841,579, issued Nov. 24, 1998 to Bloom et al., entitled "Flat Diffraction Grating Light Valve," and in U.S. Pat. No. 5,661,592, issued Aug. 26, 1997 to Bornstein et al., entitled "Method of Making and an Apparatus for a Flat Diffraction Grating Light Valve." Linear arrays of GLV devices can be used for display and printing as described in U.S. Pat. No. 5,982,553, issued Nov. 9, 1999 to Bloom et al., entitled "Display Device Incorporating One-Dimensional Grating Light-Valve Array." With linear GLV arrays of this type, the diffraction direction is not perpendicular to the array direction, which increases the complexity of the optical system required for separation of the diffracted orders. Furthermore, the active region of the array is relatively narrow requiring good alignment of line illumination over the entire length of the array, typically to within 10-30 microns over a few centimeters of length. The line illumination then also needs to be very straight over the entire linear array.
There is a need therefore for a linear array of grating devices that has a large active region with the diffraction direction perpendicular to the array direction. Furthermore, the device must be able to diffract light efficiently at high speed into discrete orders and the device fabrication must be compatible with CMOS-like processes.